The present invention is directed to the field of low dielectric constant materials produced by chemical vapor deposition (CVD) methods. In particular, the present invention is directed to methods for making films of such materials and their use as insulating layers in electronic devices.
As integrated circuit dimensions shrink, the property requirements for porous dielectric or interlayer dielectric (ILD) materials become more rigorous. In particular, any structural damage incurred during the patterning process can cause critical dimension shift in ILD features. Therefore a need exists to provide porous ILD materials that can withstand patterning with reduced or limited damage. It has been shown previously that increasing the total carbon content in the low k film can provide better damage resistance and retention of key properties. One of the means to do this is to increase methyl or methylene content in the film, however these methods can have an unfavorable impact on mechanical properties. Providing a method for increasing the total carbon content of the ILD film while retaining sufficient mechanical properties is enabling for the manufacture of next generation integrated circuits.
A process of making a silicon-containing porous film is known in which a broad variety of porogen precursors are claimed, including a family of partially or fully unsaturated organic molecules which includes aromatic species.
It is known that aromatic precursors, such as: toluene and xylene, can be used to make amorphous carbon insulating or hardmask films. In these applications, the films are thermally stable up to 400° C. and higher. For example, the prior art describes the use of amorphous carbon or fluorinated carbon films with dielectric constants of 2.3-2.4. The prior art discloses carbonaceous films from a variety of partially or fully unsaturated precursors. In both inventions, the precursors are used independently from an organosilicon backbone; and unlike the present invention, the organic material is not liberated to form a porous film. In addition, amorphous carbon films are known to provide poor mechanical properties rendering them unsuitable for an interlayer dielectric material.
The prior art describes the use of 1,3,5 trimethylbenzene as a porogen precursor for porous organosilicate films. The prior art relies on the use of thermal post-treatment to liberate the organic material.
The role or benefit of these aromatic reactive substances compared to other reactive substances is not specified.
The prior art also identifies the use of various porogen precursors, including cymene and carene in combination with silicon-containing precursors and an oxidant are described. The oxidative species, such as N2O, are used in 10× excess of the silicon-containing precursor, in order to promote oxidation. In addition, the invention relies of the use of thermal post-treatment to liberate the organic material.
Finally, the prior art also describes a method for producing a three phase dielectric film where the first phase is an organosilicate backbone, the second phase is comprised of CHx, and the third phase is comprised of air-filled pores. The result is a carbon-rich film which can provide dielectric constants of k=2.8 and above. The prior art details the results of fourier transform infrared spectroscopy (FT-IR) peak integration, which show that the CHx hydrocarbon content of the invention is up to 20× greater compared to films generated without the use of an organic precursor. In contrast, the present invention demonstrates dielectric constants below k=2.6 and a non-hydrogen containing carbon rich phase as evidenced by FT-IR analysis. The result is a superior combination of electrical, mechanical, and integration properties compared to prior art.
Prior art U.S. Pat. No. 6,312,793; U.S. Pat. No. 6,583,048; U.S. Pat. No. 6,846,515; U.S. Pat. No. 7,098,149; US 2004/0063336; US 2005/0227502; US 2006/0160374; US 2007/0141829; EP794569 and WO2008/015533 are also considered relevant.
In contrast to the above prior art, a key aspect of the present invention, described below, is to deposit a porogen-derived species in combination with a silicon-containing species, where greater than 50% of the porogen derived species can be readily liberated by ultra-violet radiation to form a porosity. A film with superior integration attributes such as a high total carbon content is achieved by using aromatic porogen precursors with silicon-containing precursors in combination. Preferably, the final film also has sufficient or improved mechanical properties that prevent failure during packaging.